Climatological analysis on extratropical cyclones in the middle latitudes of the Northern Hemisphere

Thesis--University of Tsukuba, D.Sc.(A), no. 876, 1991. 3. 2

Ca II K Spectral Study of an Emerging Flux Region using Domeless Solar Telescope in Hida Observatory

A cooperative observation with Hida observatory and Hinode satellite was performed on an emerging flux region. The successive Ca II K spectro-heliograms of the emerging flux region were taken by the Domeless Solar Telescope of Hida observatory. Hinode observed the emerging flux region with Ca II H and Fe I Stokes IQUV filtergrams. In this study, detailed dynamics and temporal evolution of the magnetic flux emergence was studied observationally. The event was first detected in the photospheric magnetic field signals. 3 minutes later, the horizontal expansion of the dark area was detected. And then, 7 minutes later than the horizontal expansion, the emerging loops were detected with the maximal rise speed of 2.1 km/s at chromospheric heights. The observed dynamics of emerging magnetic flux from the photosphere to the upper chromosphere is well consistent with the results of previous simulation works. The gradual rising phase of flux tubes with a weak magnetic strength was confirmed by our observation.Comment: 14 pages, 7 figure

〈Original Papers〉Modulation of diurnal precipitation occurrences observed in the Tibetan Plateau during monsoon season of 1998

Relations between the diurnal change of the radar echo areas and surface condition were examined at the central Tibetan Plateau during the monsoon season in 1998. During the late June, under the synoptic conditions of prevailing surface heat low with Tibetan anticyclone, a weekly time scale modulation was clearly observed in the diurnal changes of the convective activity, such as the delay of the daytime precipitation clouds toward evening, especially over the southern mountainous areas. The feature was confirmed by the diurnal weather changes indicated by multiple surface meteorological elements. Surface energy flux and hydro-meteorological measurements showed that the modulation was associated with weekly scale reducing of morning sensible heating and suppression of the planetary boundary layer development during midday. The increase of soil-surface moisture in the morning was also confirmed by the surface albedo measurements. Therefore, we hypothesize the cause of the delay of daytime precipitation by land-surface moistening due to precipitation in the previous days

Weather Divide in Winter Season in Japan Analyzed by AMeDAS Data

The distribution of weather divides in Japanese winters was identified using 30-year data of the Automated Meteorological Data Acquisition System (AMeDAS) operated by the Japan Meteorological Agency. Two kinds of weather divide were defined, one is a cloudy weather divide(CWD) determined by the high-frequency grids of large gradients in the sunshine duration distribution, and the other is a precipitation area border(PAB) where the edge of daily precipitation areas frequently appeared. The CWD appeared continuously in eastern Japan along the Pacific backbone ranges, but it was discontinuous in the central mountain ranges and western Japan. The CWD also appeared in Pacific coastal areas, such as east ofKamikouchi, south of the Kii Peninsula, and southeast of Shikoku Sanchi. The PAB overlapped with the CWD distribution in eastern Japan, and it was enhanced throughout the Sekigahara-Tamba Kochi and Chugoku Sanchi areas, but the CWD in pacific coastal areas was not associated with the PAB. Most of the weather divides were caused by the winter monsoon pressure pattern, and some PABs in northwestern Tohoku and Hokkaido areas occurred with passing pacific coastal extratropical cyclones. The distribution of the weather divides in cold-winter years was dependent on the dominance of Satoyuki/Yamayuki weather patterns, and weather divides became unclear in warm winters

〈Original Papers〉Continuous heavy precipitation with a winter occluding cyclone captured by GPM satellite in central Japan

A fifth highest event of two-day accumulation precipitation in Honsyu area (Jan. 17-18, 2016) was nominated during the 10 winters since 2006 (Anzai and Ueno, 2018). Then, using Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) products, a case study was conducted to reveal the three-dimensional and synoptic scale structures of a precipitation system associated with a cyclone the mature stage. The disturbance in the front was composed of wide-ranging stratiform precipitation with a maximum of more than 2 km level by a poleward-ascending warm airstream moving over an easterly cold air mass. Subsequent convective precipitation was associated with an upper front due to dry intrusion over the warm conveyor belt. Successions of the stratiform to areas of convective precipitation were confirmed by surface weather radar images. We clarify that the combination of stratiform and convective precipitation was dependent on the conveyor belt structure of the cyclone toward the occluding stage and caused exceptional slow-moving heavy precipitation in central Japan